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The term galaxy interaction is a general term for the effects that galaxies have on each other when the are near or colliding (interacting galaxies). The term is also used for the event (i.e., the close pass or collision) producing the effects. Gravity between them has effects, but also of interest are non-gravitational effects such as the ram pressure of clouds associated with the galaxies. The term may be used for such effects occurring during stages of galaxy mergers or galaxies passing through each other without merging.
Among the effects of galaxy interaction are stars pulled away from their previous "usual" position, e.g., resulting in stellar streams and/or tidal tails. The term galaxy harassment is used the cumulative effects of such galaxy interaction from a number of passing small galaxies.